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Regional tectonics of the Coso geothermal area along the intracontinental plate boundary in central eastern California: Three-dimensional V_p and V_p/V_s models, spatial-temporal seismicity patterns, and seismogenic deformation

Hauksson, Egill and Unruh, Jeffrey (2007) Regional tectonics of the Coso geothermal area along the intracontinental plate boundary in central eastern California: Three-dimensional V_p and V_p/V_s models, spatial-temporal seismicity patterns, and seismogenic deformation. Journal of Geophysical Research B, 112 (B6). Art. No. B06309. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20130306-152850031

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Abstract

We synthesize the tectonics of the southern Walker Lane belt and Coso Range in central eastern California using regional earthquake data. First, we invert for three-dimensional models of the V_p and V_p/V_s structure of the upper and middle crust. Using these models, we also determine three-dimensional Vs and Poisson’s ratio models. The changes in seismic velocities across the region are small, except for low velocities in sedimentary basins and a ∼2-km positive elevation of the basement velocities (V_p > 6 km/s) beneath the southern Sierra Nevada. Localized low-V_p and low-V_s zones beneath the central Coso Range image a geothermal reservoir at 0- to 3-km depth, as well as distinct low-velocity anomalies in the depth range of ∼8 to ∼12 km. Because the V_p/V_s has average crustal values within this broader zone, we interpret the anomaly to indicate a zone of few percent geothermal brines extending from 8- to 12-km depth. In addition, an embedded highly localized poorly resolved zone (possibly as small as 1 km^3) of slightly above average V_p/V_s and higher Poisson’s ratio is a tentative suggestion of a small volume percent of magma present at depth of ∼10 km. Second, we relocated the seismicity in the region using absolute traveltimes and differential traveltimes determined from waveform cross correlation. The relocated seismicity forms several spatially clustered lineaments along the southeast side of the Sierra Nevada and in the Indian Wells Valley and vicinity of the Coso geothermal field, which coincide with mapped late Quaternary faults in the region. The base of seismicity shallows from a regional depth of about ∼11 to ∼5 km beneath the central Coso Range, which we interpret as evidence for shallowing of the brittle-ductile transition zone beneath the geothermal field. In addition to abundant background seismicity, two large earthquake swarms, located 5 to 8 km to the west of Coso, occurred in April to May 1992 and May to June 2001. Two dual main shock-aftershock sequences also occurred as follows: the 1994 sequence near Ridgecrest and the later Coso earthquake sequence from late 1996 to early 1998, with the pairs of main shocks spaced 47 days and 16 months apart, respectively. Kinematic analysis of the focal mechanisms indicates that the crustal stress loading process varies across the region. The low-Vp anomaly, abundant seismicity, and crustal thinning provide quantitative evidence for the Coso region being an extensional releasing step over between two northwest-striking dextral faults: The Little Lake and Airport Lake fault zones to the south, and the Owens Valley fault to the north.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2006JB004721DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/2006JB004721/abstractPublisherArticle
ORCID:
AuthorORCID
Hauksson, Egill0000-0002-6834-5051
Additional Information:© 2007 American Geophysical Union. Received 29 August 2006; revised 21 January 2007; accepted 27 February 2007; published 26 June 2007. This study was funded by the US Navy Geothermal Program Office (contract number N68936-02-C-0207) as well as U.S. Geological Survey Grants 05HQGR0040, 06HQGR0052, and 07HQGR0048 to Caltech. We thank the JGR reviewers and the associate editor for constructive reviews. Most figures were done using GMT [Wessel and Smith, 1991]. Contribution 9154, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
U.S. NavyN68936-02-C-0207
USGS05HQGR0040
USGS06HQGR0052
USGS07HQGR0048
Subject Keywords:Seismotectonics; Coso; Geothermal; Eastern California; crustal fluids; magma chamber; Walker Lane belt; tomography; crustal deformation
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences9154
Issue or Number:B6
Record Number:CaltechAUTHORS:20130306-152850031
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130306-152850031
Official Citation:Hauksson, E., and J. Unruh (2007), Regional tectonics of the Coso geothermal area along the intracontinental plate boundary in central eastern California: Three-dimensional Vp and Vp/Vs models, spatial-temporal seismicity patterns, and seismogenic deformation, J. Geophys. Res., 112, B06309, doi:10.1029/2006JB004721.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37355
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:07 Mar 2013 00:28
Last Modified:03 Oct 2019 04:47

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